In many conventional weaving machines, a dobby is used in which the patternlike control is effected by a pattern card with control points which are holes and nonperforated points and are read by reading members, the pattern card moving in front of the reading members.
In order to make the tying of warp threads easier or to equally tension these during a longer standstill of the weaving machine, it is preferable that the heddle frames be synchronized or levelled, namely, that they be placed at the same level, wherein the warp threads do not form a shed and all heddle frames can assume their highest or lowest positions or a position which lies therebetween.
In the case of punched-card-controlled dobbies, various methods are used to synchronize the heddle frames, including the following.
In one method, a thin sheet metal plate or a piece of imperforate card material is inserted between the pattern card with the perforated and nonperforated points and the reading needles. After this, the machine is permitted to run slowly until all heddle frames are in the lower shed position, namely, all needles have read a nonperforated point.
In a second method, all reading needles are lifted off from the card by one collective member, for example during the card indexing, and are held in this position until the slowly running machine has moved all heddle frames into the lower shed position. The lifting off of the reading needles is comparable to the reading of a nonperforated point.
In a third method, the card cylinder is moved directly away from the reading needles, so that they no longer can read the pattern card. Since this corresponds to the reading of a hole by every needle, all heddle frames move into the upper shed position as soon as the machine is operated for at least one pick or read.
In a fourth method, all draw hooks are suspended or removed manually by the same draw knife of a Hattersley dobby, through which one obtains the upper or lower shed positions of all the heddles frames.
A condition for achieving the desired synchronization by these methods is that the machine must be operated for at least one pick after the corresponding control manipulation of the reading needles. However, this has the result that the card cylinder which carries the pattern card is indexed in the normal manner. Thus, prior to resuming the weaving operation, the pattern card, namely the card cylinder with the dobby and the weaving machine, must be physically reset to the proper position, since otherwise the pick-logical or proper sequential operation is lacking because at least one pick following the last-entered pick prior to the synchronizing of the heddle frames will be skipped. The careful and exact adjustment of the cards requires a relatively large time input, and in cases of lack of proficiency or carelessness, errors can also occur.
The purpose of the invention is to carry out the synchronization or levelling of the heddle frames in a manner so that the continuation of the weaving operation occurs automatically and pick-logically without the need, prior to restarting the dobby, to manually reset the pattern card to the last-entered pick.